Plant–soil feedbacks promote negative frequency dependence in the coexistence of two aridland grasses

Abstract

Understanding the mechanisms of species coexistence is key to predicting patterns of species diversity. Historically, the ecological paradigm has been that species coexist by partitioning resources: as a species increases in abundance, self-limitation kicks in, because species-specific resources decline. However, determining coexistence mechanisms has been a particular puzzle for sedentary organisms with high overlap in their resource requirements, such as plants. Recent evidence suggests that plant-associated microbes could generate the stabilizing self-limitation (negative frequency dependence) that is required for species coexistence. Here, we test the key assumption that plant-microbe feedbacks cause such self-limitation. We used competition experiments and modelling to evaluate how two common groups of soil microbes (rhizospheric microbes and biological soil crusts) influenced the self-limitation of two competing desert grass species. Negative feedbacks between the dominant plant competitor and its rhizospheric microbes magnified self-limitation, whereas beneficial interactions between both plant species and biological soil crusts partly counteracted this stabilizing effect. Plant-microbe interactions have received relatively little attention as drivers of vegetation dynamics in dry land ecosystems. Our results suggest that microbial mechanisms can contribute to patterns of plant coexistence in arid grasslands.

Effects of soil microbes on plant competition: a perspective from modern coexistence theory

“…Comparing density treatments in conditioned soil to the same treatments in sterilized soils captures the effect of all soil microbes, since the reference soil should contain virtually no microbes. This might be a suitable choice for studies that wish to isolate the impacts of soil microbes and compare the strength of microbial effects to other processes (Chung and Rudgers , which asked whether soil microbes promoted plant coexistence). One the other hand, unconditioned soils may harbor microbial propagules such as dormant spores (Lennon and Jones ) that could potentially affect the focal plant.…”

“…, Bever ). Differences in the way competing plants interact with soil microbes might promote plant coexistence (Bever , Chung and Rudgers ). Alternatively, soil microbes could favor certain plants over their competitors, creating variation in species' relative abundance (Klironomos , Mangan et al.…”

Climate sensitivity functions and net primary production: A framework for incorporating climate mean and variability

“…3) suggested that increased interannual CV in climate under a changing mean may be an overlooked, but important driver of the Great Plains to Chihuahuan Desert grassland transition. Thus, greater temporal variance in climate under a changing mean climate may explain the grassland ecotone enigma, where the competitively inferior black grama (Peters andYao 2012, Chung andRudgers 2016) appears to be replacing its more competitive congener, blue grama (Collins and Xia 2015). 3B).…”

Connecting plant–soil feedbacks to long‐term stability in a desert grassland

“…, Pendergast et al. , Chung and Rudgers ). Furthermore, experiments are typically conducted in artificial environments, which are disconnected from the dynamics of species in natural landscapes (but see Burns and Brandt , Pellkofer et al.…”

“…). Such feedbacks could increase the magnitude of negative intraspecific interactions relative to interspecific interactions, potentially stabilizing species coexistence and slowing successional change (Burns and Brandt , Chung and Rudgers ). Alternatively, plant–soil feedbacks could promote directional change in plant community composition, if feedbacks favor the establishment of later‐successional species (Kardol et al.…”